In manufacturing electronic devices such as semiconductor devices and the like, a plasma processing apparatus is used. The plasma processing apparatus generally includes a chamber main body, a mounting table and a high frequency power supply. An inner space of the chamber main body defines a chamber. The mounting table is provided in the chamber and includes a lower electrode and an electrostatic chuck. The high frequency power supply is connected to the lower electrode. In the plasma processing apparatus, a processing gas is supplied into the chamber and is excited, so that a target object mounted on the electrostatic chuck is processed.
Further, in the plasma processing apparatus, a heater may be embedded in the mounting table in order to control a temperature of the target object. The heater is connected to a heater controller having a power supply (AC power supply). In this plasma processing apparatus, a filter is installed between the heater and the heater controller in order to prevent a high frequency power supplied to the mounting table from entering the heater controller. Japanese Patent Application Publication Nos. 2011-135052 and 2015-173027 disclose techniques using a distributed constant type filter as the aforementioned filter.
The filter disclosed in Japanese Patent Application Publication No. 2011-135052 includes a coil, a capacitor, and a cylindrical conductor. The coil has windings wound at a plurality of pitches having the same length in an axial direction. In other words, the windings of the coil are wound at regular pitches. The coil is connected in parallel to the capacitor. The cylindrical conductor surrounds the coil. In frequency-impedance characteristics of the filter, impedance peaks occur at regular intervals in a frequency direction. In other words, the filter has a plurality of resonance frequencies.
As in the case of the filter disclosed in Japanese Patent Application Publication No. 2011-135052, the filter disclosed in Japanese Patent Application Publication No. 2015-173027 includes a coil, a capacitor, and a cylindrical conductor. In this filter, one or more pitches among a plurality of pitches provided by the windings of the coil in the axial direction are different from other pitches. In other words, the windings of the coil are wound at irregular pitches. By using this coil having the windings of irregular pitches, the filter can makes a specific resonance frequency among a plurality of resonance frequencies coincide with or close to a desired frequency.
As described above, a specific resonance frequency can be changed by replacing a coil having regular pitches with a coil having irregular pitches. However, a maximum value of variation of the resonance frequency which can be realized by replacing the coil having regular pitches with the coil having irregular pitches is limited. Therefore, when there is a large difference between the resonance frequency and the desired frequency, it is difficult to reduce such a large difference even by using the coil having irregular pitches.